THE ANATOMY OP ALCTONIUM DIGITATUM. 379 



Gemmation. — The buds of Alcyouium digitatum arise 

 in the canals near the surface of the colony, which run in the 

 mesogloea between the coelentera of the polyps. There seems 

 to be no definite law governing their appearance, as they 

 appear quite irregularly between the older polyps in all stages 

 of the growth of the colony. On referring to Marshall's 

 manuscript notes on the gemmation ofAlcyoniumpalmatum 

 I find a similar remark with regard to that species. The first 

 rudiment of the bud is a diverticulum from the canal in the 

 direction of the surface of the colony. The cells lining this 

 diverticulum proliferate rapidly, and it is usually found to be 

 almost filled up with loose cells. The diverticulum increases 

 in size and becomes pouched. In the older buds there are 

 undoubtedly eight of these pouches, but 1 have not been able 

 to follow the order of their formation (fig. 46). The intervals 

 between the pouches become the mesenteries of the polyp. 

 At the time of the formation (fig. 46) of the pouches an 

 invagination of the superficial ectoderm immediately above the 

 bud rudiment. This ectodermic invagination sinks down, and 

 opens eventually into the centre of the endodermic diverticulum 

 from the canal (fig. 47) . 



The later stages are very much more difiicult to follow, as it 

 is extremely difficult to obtain sections that run exactly 

 parallel with the central axis of the young polyp. In very 

 young colonies — and these are the most favorable for the study 

 of gemmation — the axis of the bud rudiment is by no means 

 parallel with the axis of the neighbouring polyps, and conse- 

 quently it is impossible to orient the colony before embedding ; 

 and in older colonies the young buds occur at such rare 

 intervals that hundreds of slides of sections may be hunted 

 through without furnishing abud in such a condition as will lead 

 to any important results. There can be no doubt, however, 

 that the epithelium of the stomodseum is formed from the cells 

 of the ectodermic invagination. 



As in Kenilla, so in Alcyonium, the two dorsal mesenterial 

 filaments are the first to be developed, and for a long time 

 apparently these filaments are the only ones to be fouud in the 



